PROFESSOR OWEN ON THE FOSSIL MAMMALS OF AUSTRALIA. 
265 
§ 7. Sthenurus Atlas. — Similar considerations to those which influenced judgment 
and action in regard to the type fossil of Macropus Titan , added to plainer indications 
of the incomplete development of the rear teeth of the molar series in the fragment 
under scrutiny, led me, in 1837, to perform the same operation on the subject of fig. 4, 
Plate XXII. * ; and great was my surprise at the result. 
The hidden germ (p 3) equalled in antero-posterior diameter both the deciduous molars 
which it would have displaced, and surpassed in that diameter the largest of the molars 
to the extent of one half that length of their crown. For the great extinct species of 
Kangaroo so indicated I proposed the name of Macropus Atlas f. 
The tooth so discovered recalled a dental characteristic of the Potoroos, or Kangaroo- 
rats ( Hypsyprymnus , &c) ; but the molars in the fossil were strictly bilophodont, more 
so, indeed, than in Macropus Titan or the existing Macropus major. There was less 
indication, for example, in the “ links ” of any subdivision or reduction of the two trans- 
verse ridges to a quadrituberculate grinding-surface ; they stood out more definitely 
and more freely. Moreover, the large premolar of the fossil was primarily divided exter- 
nally into a fore lobe and hind lobe by a vertical fissure continued as a groove almost 
to the base of the crown, whilst the oblique extension of that fissure inward and backward 
gave a transversely subbilobed character to the unworn surface of the hinder part of 
the tooth. As, however, I have since obtained a portion of the upper jaw with the right 
series of molars of the same species, I will proceed with its description before entering 
upon further and requisite details of the mandibular evidences originally indicating the 
present extinct subgenus of Kangaroo. 
The instructive illustration of the maxillary dentition of Sthenurus Atlas (Plate XXIV. 
figs. 4, 5, 6) formed part of a collection of fossils sent to me by F. G. Waterhouse, Esq., 
Cor.M.Z.S., Curator of the Museum of Natural History in Adelaide, South Australia, 
in the freshwater deposits of which province this fossil was obtained. 
The portion of maxilla includes the masseteric process (ib. fig. 4, 21 '), the hind border 
of the maxillary pier from which it is continued being parallel to the interval between 
the penultimate ( m 2 ) and last ( m 3) molars. The process extends down a little below 
the alveolar border of m 2 , and appears to be entire with an obtuse end. It is not so 
long relatively, does not reach so low, as in Macropus major or Macropus ( Osphranter ) 
robustus, but is more produced than in Macropus ( Halmaturus ) ualabatus : its propor- 
tions are most nearly those of Macropus ( Phascolagus ) erubescens. The outer surface 
of the base of the process is less deeply excavated than in any of the above-named recent 
species. 
The convex tract behind the masseteric process and maxillary pier of the zygoma 
leads into the orbit, and there, about 8 lines in advance of the hind border of the pier, is 
the orbital aperture of the suborbital canal. It is single, subcircular, well defined, 
without any appearance of the oblong depression we there see in Macropus , Osphranter , 
and Halmaturus , where a second large foramen also communicates with the orbit. 
* Plate xxix. fig. 1, Mitchell’s * Three Expeditions,’ &c., vol. ii. 1838. + Ibid. p. 359. 
